GIRDER MOUNTAIN BIKE FORK
A thesis submitted to the Faculty of the Mechanical Engineering Technology Program of the University of Cincinnati in partial fulfillment of the requirements for the degree of
Bachelor of Science
in Mechanical Engineering Technology at the College of Engineering & Applied Science
by
RYAN LINDENBERGER
Bachelor of Science University of Cincinnati
May 2012
Faculty Advisor: Amir Salehpour
ACKNOWLEDGEMENTS
I would like to personally thank Professor Amir Salehpour for continually pushing me during the design phase of this project. He helped me see problems that I might encounter with a given design or loading condition. This was especially helpful in establishing a realistic worst case loading condition.
My gratitude goes out to Nicholas Plataniotis. Without his machining and welding knowledge this project would have been significantly more difficult.
I would also like to thank all of my friends and family that helped with the manufacturing and testing of the fork. Without their support none of this would have been possible.
ii
TABLE OF CONTENTS
GIRDER MOUNTAIN BIKE FORK ...... 1 ACKNOWLEDGEMENTS ...... II TABLE OF CONTENTS ...... III LIST OF FIGURES ...... V LIST OF TABLES ...... V ABSTRACT ...... VI PROBLEM DEFINITION AND BACKGROUND ...... 1 RIGID FORK DESIGN ...... 2 GENERAL TELESCOPING FORK DESIGN ...... 3 GENERAL GIRDER FORK DESIGN ...... 5 RESEARCH ...... 8
EXISTING GIRDER MOUNTAIN BIKE FORKS ...... 8 CUSTOMER FEADBACK ...... 10
INTERVIEW ...... 10 CUSTOMER SURVEY ...... 10 HOUSE OF QUALITY ...... 11 PRODUCT OBJECTIVES ...... 14 DESIGN ALTERNATIVES AND SELECTION ...... 16
DESIGN 1 ...... 16 DESIGN 2 ...... 17 DRAWINGS ...... 20 LOADING CONDITIONS ...... 36 DESIGN ANALYSIS ...... 38
HAND CALCULATIONS ...... 38 COSMOS SIMULATIONS ...... 40 FACTORS OF SAFETY OF CONCERN ...... 44 COMPONENT SELECTION ...... 47 BILL OF MATERIALS ...... 48 PROTOTYPE BUDGET ...... 49 SCHEDULE ...... 51 MANUFACTURING ...... 52
MACHINING ...... 52 WELDING ...... 55 PLASMA CUTTING ...... 57
iii
DESIGN MODIFICATIONS ...... 59 HIGH VOLUME PRODUCTION ...... 60 TESTING ...... 61 CONCLUSION ...... 65 WORKS CITED ...... 66 APPENDIX A - RESEARCH ...... 1 APPENDIX B – CUSTOMER SURVEY AND RESULTS ...... 1 APPENDIX C – QUALITY FUNCTION DEPLOYMENT ...... 1 APPENDIX D – PRODUCT OBJECTIVES ...... 1 APPENDIX E – SCHEDULE ...... 1 APPENDIX F – PROTOTYPE BUDGET ...... 1
iv
LIST OF FIGURES Figure 1: Common Mountain Bike Forks ...... 1 Figure 2: Rigid Fork...... 2 Figure 3: Telescopic Fork ...... 3 Figure 4: Telescopic Fork Cut Away ...... 4 Figure 5: Typical Girder Fork Layout ...... 5 Figure 6: Steering Geometry ...... 6 Figure 7: Yamaha R1 with Custom Girder Fork ...... 7 Figure 8: Girvin Fork ...... 9 Figure 9: Design 1 ...... 16 Figure 10: Design 2 ...... 17 Figure 11: FOURBAR Program ...... 18 Figure 12: Design 2 Suspension Travel ...... 19 Figure 13: Loading Conditions ...... 37 Figure 14: Lower Link Stress ...... 40 Figure 15: Lower Link Displacement ...... 41 Figure 16: Lower Block Stress ...... 41 Figure 17: Lower Block Displacement ...... 42 Figure 18: Upper Block Stress ...... 42 Figure 19: Upper Block Displacement ...... 43 Figure 20: Fork Sub-Assembly Stress & Displacement ...... 44 Figure 21: Upper Shock Mount Stress ...... 45 Figure 22: Upper Shock Mount Displacement ...... 46 Figure 23: Setting the 0,0 for a part ...... 52 Figure 24: Slitting Saw on a Horizontal Mill...... 53 Figure 25: Damaged Part and Broken Slitting Saw ...... 54 Figure 26: Turning a Brake Pin ...... 54 Figure 27: Self feeding Die Tail Stock ...... 55 Figure 28: Initial Weld Set-up ...... 56 Figure 29: Welding Fork Sub-Assy ...... 56 Figure 30: Upper Block Weld Set-up ...... 57 Figure 31: CNC Plasma Cut Components ...... 58 Figure 32: Plasma Cut vs. Machined Edge ...... 58 Figure 33: Fork Wobble Direction ...... 62 Figure 34: Weighing the Fork ...... 63 Figure 35: Fork Installed on Bike ...... 63
LIST OF TABLES Table 1: Customer Importance Ratings ...... 11 Table 2: Quality Function Deployment ...... 12 Table 3: Bill of Raw Materials...... 48 Table 4: Prototype Budget ...... 49 Table 5: Final Prototype Cost ...... 50 Table 6: Schedule ...... 51
v
ABSTRACT
The idea for the girder mountain bike fork came about as a proof of concept for a high performance girder motorcycle fork. The project was applied to a bicycle for several reasons. First of was cost. Secondly it would be a safe test platform to develop an understanding of how to manipulate the steering geometry to get the required results. It also provided a safer alternative to see what forces were at play.
The girder design was chosen because it separated the steering and suspension aspects of the fork. It has all the positives of a ridged fork while still retaining suspension. Girder forks were once the primary fork used in the motorcycle industry. However as the telescopic fork became cheaper and easier to manufacture it fell by the wayside. As a result there are no high performance girder motorcycle forks except for a few custom made examples.
Research shows that there were several companies in the past that manufactured girder mountain bike forks. They have gone out of business for a variety of reasons. Most notably the poor shock that was used and the unconventional “J” suspension travel. This proved to be a valuable learning tool. As a result the fork developed for this project closely mimics that of a stock telescopic fork in terms of steering geometry and suspension travel. Testing showed that those that used the fork saw very little difference in terms of handling between the prototype and what they were used to. The girder design also adsorbs the terrain differently than a telescopic fork. There is smoothness and softness when hitting bumps where as the telescopic fork has more of a sharp jolt.
Based on the manufacturing cost and test results it would be entirely plausible to develop a high performance girder mountain bike fork that everyone from the average rider up to the pros could enjoy. If there is one thing that this project did a superb job of showing that there is always room for improvement. Just because a particular technology is considered outdated does not mean that it can be made to be a contender.
vi Girder Mountain Bike Fork Lindenberger
PROBLEM DEFINITION AND BACKGROUND
Throughout the history of two-wheeled transportation there have been a variety of fork designs for both motorcycles and bicycles. The most popular of these designs are ridged, springer, girder, and telescoping. An example of some of these forks can be seen in Figure 1. Each of these describes how the front suspension operates. A ridged for is a solid unit and does not have any suspension. By its very nature it is the cheapest and most robust design (1). A springer fork uses a series of connecting bars and linkages. Springer forks are the most complicated design and were not considered for this project because of this. A girder fork uses solid fork tubes connected to a four bar linkage (2). Telescoping forks have one tube riding inside of another and internal springs to actuate the suspension (3).
Figure 1: Common Mountain Bike Forks
Figure 1shows the two most common forks as well as a girder fork for mountain bike. All three will be explained in detail in the following sections.
In the case of this project, the primary competitors to the girder design are ridged and telescoping forks for mountain bikes. Furthermore this project focuses on a suspension style fork which completely eliminates the ridged fork from consideration. There are pros and cons to each system which will be explained in the following sections.
The purpose of this project is to provide a proof of concept for a performance orientated girder suspension fork for a motorcycle. A mountain bike was chosen due to cost constraints as well as to provide a safe platform to develop the proper suspension geometries. While there are some commercially available girder forks for motorcycles most are designed as factory replacements for antique motorcycles. Most are not designed with high performance in mind. Most performance oriented girder forks are custom one off products or only produced in extremely limited quantities.
1 Girder Mountain Bikee Fork LindenbergerLind
RIGID FORK DESIGNIGN
Rigid forks are the simpleimplest forks on the market. They are called rigidid becausebec they are one solid unit and containn no mmoving pieces. Due to their design rigid forksrks arear the simplest and least expensive kind of forfork that can be produced. The fork in Figuree 2 isis producp e from CroMoly steel. This is considernsidered a high strength and somewhat exotic materiaaterial, but due to the simple design of the ridged fork cost only $80.
Figure 2: Rigid Fork
While the rigid is thee mosmost widely produced bicycle fork it does not qualifyqualif as a competitor for this projectct due to its lack of suspension. In addition to that motorcyclesmo have not used rigid forks for nearlyearly one hundred years. With this being a prooff of conceptco project it must be rejected.
2 Girder Mountain Bike Fork Lindenberger
GENERAL TELESCOPING FORK DESIGN
A trip to any bicycle or motorcycle shop will show that the telescoping suspension fork is the only commercially available suspension fork on the market. This is because they are relatively inexpensive and simple to manufacture and provide good performance for rider’s right out of the box.
However there is always room for improvement. There are some major downfalls of the telescoping fork design. For instance, damaged fork tubes will generally disrupt the suspension function of the fork. One damaged component may also require that the entire fork be replaced. Seeing as adjustable performance forks can run anywhere from $300 to $1700 for a mountain bike, a small accident could lead to costly repairs (3). For instance should the ridged or telescoping section of the fork shown in Figure 3 be dented, gouged or otherwise damaged this $1600 dollar fork would be scrap.
Ridged Fork Tube Section
Internal Dampening System
Telescoping Fork Tube Section
Figure 3: Telescopic Fork
3 Girder Mountain Bike Fork Lindenberger
A telescoping for fork has two tubes per side that act as the suspension. One tube rides inside the other. Springs can be either internal or external. The actual dampening system may consist of coil springs, air spring or a combination of both. These features are generally driven by manufacturer and cost. Regardless of the mechanism the two tubes in contact must have tight tolerances for the fork to be sturdy. If the fork uses an air shock then the tolerance must be that much tighter to keep air from leaking past any seals.
Figure 4 shows the internal workings of a typical telescopic fork. From this figure it is easy to see why strict tolerances must be applied. The right side of the fork contains a coil spring that controls most of the suspension travel while the left side contains an air dampening system to eliminate any harmonic vibrations.
Typical Failure point
Ridged Fork Tube Section
Internal Dampening System
Telescoping Fork Tube Section
Figure 4: Telescopic Fork Cut Away
4 Girder Mountain Bike Fork Lindenberger
GENERAL GIRDER FORK DESIGN
In today’s world the girder fork has fallen by the wayside due to advances in technology that made telescopic forks more economical. However there are several reasons to use girder suspension forks. The solid fork tubes are one such advantage. Girder forks provide a very rigid design while still having suspension travel. In addition to sturdy fork tubes, girder forks also provide some protection to the shocks and springs. This is because the shock is typically located inside the linkage system. This can be seen in Figure 5. Impacts that might damage the suspension of a typical telescoping fork are less of a concern with the girder design. In addition to these features girder forks also allow the designer to tailor the path that the wheel follows during suspension travel (4). Telescoping forks can only move linearly along the axis of the fork tube.
Girder forks function by using a four bar linkage to achieve suspension travel. The tolerances must still be tight, but the fit up of the links themselves doesn’t control the actual dampening of the system. This is achieved by using a prebuilt shock.
Fixed Points Suspension
Travel Active Links
Forks move as one unit
Figure 5: Typical Girder Fork Layout
Despite the positives of the girder design there are still several drawbacks to the system. The most notable drawback of girder forks is that they are more complex than that of the telescoping layout. Due to their design girder forks are also not as compact as their telescoping counterparts. Trail loss is another major concern with the girder design. Trail is the difference between where the wheel touches the ground and where the steering axis intersects the ground (5). See Figure 6 for clarification of trail. There are many calculations that must be performed to get the correct balance of rake, trail, and head angle. This is
5 Girder Mountain Bikee Fork LindenbergerLind complicated due to that fact ththat there are no optimal numbers that can be used.used There are some general guide lines that sshould be followed so that the bike does notot havehav too little or too much wheel flop. Wheelheel flflop is how easily the front wheel will “flop”” overove when turned. Again there are no specificfic numnumbers to us. These geometric features can be easilyeas changed depending on the intendeded appapplication of the bike. Road cruisers will haveve differentdiff values for rake, trail, head angle,e, and wheel flop than a mountain bike.
Figure 6: Steering Geometry
Many of the drawbackscks of the girder design can be solved with a properoper layoutla for the application. A proper balancelance oof head angle, rake, and trail will solve mananyy of the problems associated with the girderr desigdesign. Keeping these items in balance will alsoso drivdrive the wheel flop of the bike and ultimatelyately determine how the bike handles as well ass how easy the bike is to ride. However, theree is nonot much that can be done to significantly redueducece the size of the fork without harming performarformance.
6 Girder Mountain Bike Fork Lindenberger
As previously mentioned most, if not all, high performance oriented girder forks are one off designs. This is the case with the following Yamaha R1 sport bike as seen in Figure 7. Substantial work had to be done to the frame of the motorcycle to achieve the necessary rake angle. A steep rake angle was chosen because it kept the fork more upright which lowered trail loss during suspension travel. In addition the frame side pivot points were moved behind the steering axis. This does two things for the bike.1) Increased the length of suspension travel. 2) Gives the steering a self-centering effect (5). Similar designs can be seen on many custom motorcycles with limited production runs.
Figure 7: Yamaha R1 with Custom Girder Fork
7 Girder Mountain Bike Fork Lindenberger
RESEARCH
EXISTING GIRDER MOUNTAIN BIKE FORKS
Existing manufacturers for girder mountain bike forks include Girvin, Pro-Flex, and Noleen. The layout of each company’s fork is roughly identical which is because all three companies are one in the same. For the purpose of this report all three will be referred to a Girvin forks. Little is known about these forks due to the fact that all three companies have gone out of business. By examining their design it is easy to understand why. The Girvin fork looks as if it was designed purely to be compact and astatically pleasing. The end result is a compact girder for that looks great, but has poor performance for the price. Girvin also used an elastomer shock that did not hold up will. Several online reviews stated that the elastomer simply melted while the fork was in storage over a few summers (2).
By examining Figure 8 some major design flaws can easily be seen. First and foremost the Top and Bottom links are angle downward. The downward angle means that the pivot point on the fork tube is not at the furthest point from the frame pivots along the x-axis as shown in the side view. This causes the fork to move forward during suspension travel. In essence what this means is that as the wheel of the bike comes in contact with an obstacle it must push into the object before going up an over it. This will cause an increase in the impact force on the fork. The design of the top link will also cause it to fail. The cross-section of the link is in an orientation that bending the link becomes a serious concern. Couple this poor link design with outward suspension movement and it is understandable why riders were bending this link. It is unclear as to what affect the Girvin fork had on the trail of the bike. However the path of the suspension travel would certainly lead to massive changes in the trail. This might cause some wobble in the steering at higher speeds. There is also the fact that the suspension on the Girvin forks was extremely limited. Suspension is limited to 50mm or just shy of two inches. This could limit which environments that this fork could be used in.
8 Girder Mountain Bike Fork Lindenberger
Front View Side View
Top Link
Frame Pivots Bottom Link
As the suspension is compressed the fork moves outward away from the bike as illustrated by the circles and arrows.
Fork Pivots
Y
X
Figure 8: Girvin Fork
The culmination of this research is an understanding of the problems that currently exist. As previously explained there are many features of each fork that can benefit from a redesign. To further develop a satisfactory design, customer input is required. This customer input will develop a baseline for the girder mountain bike fork. The survey focuses on a mountain bike fork as the sample pool was considered to be larger. It was also thought that mountain bike owners would have experience with several different forks on the market where as motorcycle owners may only have experience with one fork or one motorcycle for that matter.
9 Girder Mountain Bike Fork Lindenberger
CUSTOMER FEADBACK
INTERVIEW
To develop an understanding of desired customer features an interview was conducted with Matt Bliemeister. Mr. Bliemeister was chosen because he holds a Bachelor’s Degree in Engineering and was a Crew Chief and Team owner of a BXM racing team. Mr. Bliemeister stated that having standard parts is critical. A part is no good if it cannot be used on a variety of bikes. In the world of racing having quality made light weight components is essential. For the most part price follows performance and quality. However there is a point where weight becomes a major cost driver. At a certain point it might cost upwards of $800 to shave one pound of weight from a BMX bike (6).
In addition to these insights Mr. Bliemeister suggested that having quick change components is a major advantage when it comes to working on bikes between races. Quick change components basically means less time is spent working on the bike and more time can be spent making fine tune adjustments for the rider (6).
CUSTOMER SURVEY
The mountain bike aspect of the project was the focus of the survey. While this is a proof of concept for a motorcycle, it was concluded that most motorcycle riders would not have sufficient experience with different forks. This is mostly a cost issue. Motorcycles are expensive and a motorcycle having a fork other than telescoping would be even more so. However bicycle riders would have used several brands and styles of forks during their time riding. This experience would primarily be in the form of rigid and telescoping forks. This survey was distributed to students, coworkers, and friends of the writer. This was deemed a suitable sample group because of the wide variety of potential consumers within the group. This group contained avid mountain bike enthusiasts as well as the average bicycle rider. For the girder fork to become a viable option for consumers it must perform at all levels of the industry. Thirty surveys were returned resulting in a reliable result.
Of those surveyed it is clear that that durability is the most important feature consumers look for. Of that same group all were highly satisfied with the durability of their current mountain bike fork. As such this project will focus heavily on producing a modular girder suspension fork that is at least as durable as a common telescopic fork.
Easy maintenance and light weight come in second and third in terms of importance. Comparing the importance of these features to the satisfaction with current products it is clear that there is much to improve upon. Most consumers were not overly satisfied with their current fork’s ease of maintenance. This can be seen by the 3.5 rating it received. Consumers were less than satisfied with the weight of their current fork. Looking at the bulkier design of the girder will require close attention to materials and designs to keep weight down.
10 Girder Mountain Bike Fork Lindenberger
Most other features were generally important to consumers with ratings ranging from 3.2 to 4.3. Similarly consumers were generally satisfied with their current mountain bike fork with numbers ranging from 3.0 to 4.5.
Expected average price was $316. The prototype cost for the fork itself is forecasted to be around $425. It would not be unreasonable to reach a retail price in the low $300 range with the price cuts that come with bulk orders.
A full copy of the survey and the results can be found in Appendix B. It should be referenced as needed for this section of the report.
HOUSE OF QUALITY
Table 1: Customer Importance Ratings
Ryan Lindenberger GirderMountain bike Fork 9 = Strong 3 = Moderate 1 = Weak Customer Customer importance Designer's Multiplier SatisfactionCurrent SatisfactionPlanned Improvement ratio Modified Importance Relative weight Relative % weight Adjustable 3.8 1.2 3.5 4 1.1 5.3 0.12 12% Modular 3.2 1.2 3.3 4.5 1.4 5.1 0.12 12% Durable 4.8 1.0 5.0 5 1.0 4.8 0.11 11% Affordable 3.8 1.1 3.5 4 1.1 4.8 0.11 11% Work in Several Environments 4.3 1.0 3.7 4 1.1 4.7 0.11 11% Easy Maintenance 4.3 1.0 3.5 3.8 1.1 4.6 0.11 11% Light Weight 4.2 0.9 2.7 3 1.1 4.2 0.10 10% Compatible 3.5 1.0 3.0 3 1.0 3.5 0.08 8% Appearance 3.7 1.0 4.5 4 0.9 3.3 0.08 8% Compact 3.5 0.8 3.0 3 1.0 2.8 0.06 6% Abs. importance 22.5 43.2 1.0 Rel. importance 0.99
Please reference Appendix B and Appendix C for complete survey results and complete QFD during this section as required.
These numbers were adjusted by the Designer due to the face that it is unlikely that any of those surveyed will have used a similar product such as the Girvin fork. These adjustments can be seen in the “Designer’s Multiplier” and “Planned Satisfaction” columns in Table 1. This project is focused on the modular and adjustable aspect of the fork and as such the importance ratings for these were positively adjusted. Similarly the compactness of the fork will be affected by the girder design so its importance was adjusted negatively to reflect this.
11 Girder Mountain Bike Fork Lindenberger
By adjusting the customer importance ratings the Relative weight of each feature was changed. Modular and Adjustable became the most important features after adjusting the customer importance. Durability was the customer’s top priority and it remains near the top of the list after the designer’s multiplier was factored in. This drop in the importance of durability can be easily explained. It is likely that some of those surveyed use rigid forks. As mentioned in the introduction the rigid fork is the most durable design. Seeing as the girder design is more complex than the rigid design it was considered acceptable to have a drop in durability.
Table 2: Quality Function Deployment
Ryan Lindenberger GirderMountain bike Fork 9 = Strong 3 = Moderate 1 = Weak Standardized Hardware (Yes/No) Hardware Standardized Size (Inches) Cost ($) Rust Resistance Property/Surface(Material Coating) Material Strength (PSI) Sealed Bearings (Yes/No) ToolsCommon Used (Yes/No) Function after (Yes/No) Frontal Crash Person One Assembly/Disassembly (Yes/No) Less than 7 (Yes/No) pounds Edges Sharp No (Yes/No) Adjustable Size (Yes/No) Affordable 3 1 9 3 3 3 Modular 9 1 3 Light Weight 3 9 3 9 Durable 1 3 3 9 3 9 1 Adjustable 91 93 3 1 Compatible 3 9 9 Compact 9 Easy Maintenance 3 3 1 1 1 9 1 9 Appearance 1 3 9 1 9 Work in Several Environments 3 9 1 3 9 Abs. importance 3.25 2.62 2.44 2.44 2.40 2.33 1.84 1.33 1.11 1.09 0.99 0.68 Rel. importance 0.13 0.12 0.11 0.11 0.11 0.10 0.08 0.06 0.05 0.05 0.04 0.03
The engineering characteristics will define how product objectives will be accomplished. As an example from Table 2 it can be observed that using standardized hardware will heavily affect the modularity and adjustability of the fork. Affordability, compatibility, and easy maintenance are moderately affected by the use of standard hardware. The durability and appearance of the fork might be impacted by the use of standard hardware, but it is unclear as to what extent if at all. The other features were considered to not be affected by the use of standard hardware.
12 Girder Mountain Bike Fork Lindenberger
The rest of the table was filled out in the same way as the example above. Once the relationship between all of the customer features and engineering characteristics was understood a proper list of product objectives and test requirements was developed.
13 Girder Mountain Bike Fork Lindenberger
PRODUCT OBJECTIVES
Product Objectives Modular Girder Mountain Bike Fork The following is a list of proof of design agreements and how they will be obtained or measured to ensure that the goal of the project was met. The Product Objectives will focus on a modular girder suspension style mountain bike fork. It will be noted that the purchased shock is not being tested, but only fabricated items of the fork itself.
Adjustable: Relative Weight 12% 1. The fork tubes are to be replaceable with a stronger material of a specific standard size. 2. An adjustable shock will be used for suspension. Modular: Relative Weight 12% 1. The fork will offer the ability to change the fork tubes to different materials and lengths as needed by consumers 2. Standardized hardware will be used where applicable. Affordable: Relative Weight 11% 1. The fork in standard equipment will cost consumers no more than $300. Durable: Relative Weight 11% 1. The fork will be designed with an appropriate safety factor so that suspension and steering functions are not damaged after a frontal crash. Easy Maintenance: Relative Weight 11% 1. The fork will be able to be disassembled and reassembled by one person with average mechanical ability. 2. Only common tools are to be used. 3. Worn or damaged hardware will be easily available through hardware stores such as McMaster-Carr. Work in several environments: Relative Weight 11% 1. The fork shall work in normal, wet, muddy, and dusty/sandy environments a. Sealed bearings shall be used where applicable to keep debris out of moving joints b. Materials selected will not corrode or rust in these environments i. If materials may corrode, a surface finish to aid in the prevention of corrosion will be employed. Light Weight: Relative Weight 10% 1. The fork in standard equipment will weigh less than 7 pounds. Appearance: Relative Weight 8% 1. The fork is to have no sharp edges which could easily injure the rider. 2. Surface finishes used will prevent corrosion and not come off easily in day to day use. Compatible: Relative Weight 8% 1. The fork will use standard neck bearings and will work on several different bikes. a. The fork will be able to be used on bikes ranging from 20” to 29”wheel size while only replacing the fork tubes. Compact: Relative Weight 6% 1. The fork will not be bulky to the point of inhibiting the steering of the bike.
14 Girder Mountain Bike Fork Lindenberger
2. The fork will be designed to minimize the possibility of brush getting caught in the linkage.
Much of the focus of this project is on the modular and adjustable aspects of the fork. Cost is a factor, but by using standard material and hardware cost will be driven down. Durability is also impacted by the use of standard components. Several of these objectives will work together to solve the problem. Others may fight each other. For instance having a compact design might impede the adjustability of the fork. In the case of the Girvin the compact design caused a direct threat to the durability. A fine balance of each objective will be required to have a well-designed fork. Some areas will certainly not receive as much attention as others, but this is precisely why these objectives are weighted.
15 Girder Mountain Bike Fork Lindenberger
DESIGN ALTERNATIVES AND SELECTION
DESIGN 1
The initial purpose of this project was to Clamps develop a completely modular fork. As such the initial design featured a series of clamps that held the fork tubes. These tubes were to be the weak link in the system. They could be upgraded as the rider saw fit with any material the rider saw fit. This would have allowed for a wide range of adjustability for many different environments and riding conditions. Figure 9 also shows that the active links are connected to the frame behind the steering axis. This does two things for the fork. First it creates a self- centering effect on the steering, and secondly it allows the active links to be longer with Active Links increases potential suspension travel. Some
other features of this design are that the fork Fork Tubes tubes are parallel to the steering axis and the active links are of equal length. These features make manufacturing components simpler. Wheel Brackets There are however many drawbacks to this Figure 9: Design 1 design. First and foremost is its weight. As shown in Figure 9 this design weighed in at over seven pounds and that did not include brake mounts or the required hardware. All the weight came from the complicated clamping system used to hold the tubes in place. The clamps themselves also posed somewhat of a problem as they would need to be machined from solid blocks of aluminum. This would have caused long machining times and high scrap rates. Both of which would raise the cost. The wheel mounts shown would also greatly increase the trail of the bicycle which would have had a negative impact on the handling.
Looking further into the development of Design 1 it became clear that assembly of the fork would be an issue. The main concern with assembly would be the alignment and spacing of the various clamps. A series of assembly fixtures would have to be developed in order to ensure that the fork was assembled in the correct positions. For an OEM manufacturer this would not be an issue. However one of the product objectives is for the fork to be easily serviced by a person with average mechanical skills in a timely manner. This would mean supplying the customer with the same assembly fixtures which would drive cost up. From Figure 9 it is also clear to see that any maintenance on the active links would require removing the fork tubes.
16 Girder Mountain Bike Fork Lindenberger
DESIGN 2
The second design sought to eliminate as many of the downfalls of the first design as possible. The primary concerns were to lower the weight, reduce cost, and to make maintenance easier without worrying about affecting the suspension geometry. This meant removing the replaceable fork tube feature. In place of this is a fully welded fork sub- assembly that already includes all required mounts and brackets. See Figure 10 for clarification.
Brake Mounts
Active Links
Fork Tubes
Wheel Brackets
Figure 10: Design 2
Most of the components of this new design are either standard sized aluminum tubing or are easily cut from plate metal. This lowers the machining time and the cost associated with machining. The parts that do require heave machining could be easily adapted for casting to lower costs from a production standpoint. These parts include both upper and lower pivot blocks and the brake mounts. Drawings of these components can be found in the Drawings section of this report.
Design 2 also went through a geometry optimization step. This step sought to limit the change in trail. In addition to this the optimization step also sought to help the girder fork mimic the original suspension geometry.
First the basic link lengths were entered into the program FOURBAR. This program allows the user to adjust the link lengths and positions until the desired path is achieved. For this
17 Girder Mountain Bike Fork Lindenberger
application the desired path is parallel to the steering axis or at least along the axis of the fork tubes. This can be seen in Figure 11.
Suspension Travel
Fork Tube
Upper Link
Lower Link
Figure 11: FOURBAR Program
The data from FOURBAR shows that the path of the suspension travel nearly perfectly follows the axis of the fork tubes. This was considered to be a suitable starting point for the finalized suspension geometry. However, FOURBAR could not take everything into account. One such feature is the wheel mount brackets. The wheel brackets locate the wheel behind the fork tubes. This was done to position the front wheel in roughly the same position that the original fork provided. This relocates the path of suspension from that shown in the previous figure. FOURBAR also doesn’t take the head angle of the bike frame into account. Both of these factors will play a role in affecting the steering geometry of the bicycle.
18 Girder Mountain Bike Fork Lindenberger
After finalized models were created based on the data from FOURBAR, a more accurate analysis of the steering geometry was conducted. Figure 12 shows the wheel at the two extremes of the suspension path. Completely uncompressed and completely compressed.
Figure 12: Design 2 Suspension Travel
This design provides a 2.2 inch suspension travel while still using the bump stop supplied with the shock. In this condition there is a total change in trail of 0.14 inches. It may be possible to further reduce the change in trail with further optimization.
19 Girder Mountain Bike Fork Lindenberger
DRAWINGS
The following pages contain the finalized engineering drawings that will be used to fabricate the girder fork.
20 1 3 % " - *
: :
% *
3 *
-
1 )
3
1
- % " " "#$%"#&'(($))"#%% ! * ++ (, ! - ./ " "0,& (, ! % 10,&02! 3 3 ++02! *3"$*"$*3"02675 1 ) ,24 526 1%* ) %5, ! 2 5, ! 20,26 8,7 2 - 8,7 25,7 * 9',&:; *" - . *"<1<< " 1*<"$1$% .$.<<%.= ++5, ! % +' 3 3 (,2+' 1 * (,2+' 0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .:" 1 3 % " - * 1 3 % " - *
: :
" 1
* -
3
%
E %* <
E *3" < 0
:,! "#$)"#$#-* ;5( ' !7097 * -, 02! - *;5( ' !7 " :,! 526 - E E ") 3" % * '!, 27 < < "0,&5, ! 0 0 3 , 27 1 ++, 02! 0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; * ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .:" 1 3 % " - * 1 3 % " - *
: :
E *3"< E %11 <
E %" < 0
0/ 0 0>>
% ++ (, !A ) ++5, ! , 27A 0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0><;.>< .*:" 1 3 % " - * 1 3 % " - *
: : %" / 00 .
. : "#: . A : *"<1. 0>> 0>-* *"#
E -" < E ) < 0 E 3" E < " < E 0 11 < 0
E 3" <
"
1-
: / 0>> 0. ; :> 0>%%<% . ; @0 ?1? 0 > "#=1*#; 00=1-# : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .-:" 1 3 % " - * 1 3 % " - *
: : 1
E %%3<
*
*3"
/ 0>> 0>%%<% "#=%"#; 00=))"#
3" "%"
"
- 0/ 0>> 0>%%<% 3"#="#; 00="#
"%" 3"
%
0/ 0>> 0>%%<% 3"#=%"#; 00=%#
0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .":" 1 3 % " - * 1 3 % " - *
: :
E "< *3" E : *3" " <
% %
E < E -"< E E < -" < E E -*1 -*1 < <
E %11 <
E %11 < E % E : < %< E E < "-" E E < < < "-" < :<: E - E < - <
*;.0 / . *;.0 /0: 0>> 0>> 0>%%<% 0 0>%%<% 0
0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .%:" 1 3 % " - * 1 3 % " - *
: :
@
E - <
E E " < <
E %*<
E" @<@ "%* @ < " 0>
E 11 < : ". E *3" <
E 3" <
E * < E "$1'++.,( 1*"<
"0; 0/ 0>> 0>%%<% 0/
0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .3:" 1 3 % " - * 1 3 % " - *
: :
E" " < "
E %* <
E " <
E %* <
E 11 <
E 1- <
B : *3"# .
% 0/A 0>> 0>%%<% 0/
0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .1:" 1 3 % " - * 1 3 % " - *
: :
E -*3"<
<
3 0/ 0>> 0>33"<% *3"#./ 0
> 10; 0/: 0
E *3" < E = E "- " < . < E 3" *3" <
" = 3"
B :*3"# B . " 0 < E " < 10; 0/ 0>> 0>33"<% *3"#./ 0
0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .):" 1 3 % " - * 1 3 % " - *
: :
E" E E ** %* " < < " <
E *3" %* < B : *3"# .
: / . 0>> 0>%%<%
/ 00 ** **1 .
- A . . : "#: . 0>> : *"<1. 0>-* *"#
E " E < "<
E * <
30
0>> 0. ; :> 0>0 . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * C . D . 0 0 ; 0>< ;.>< .:" 1 3 % " - * 1 3 % " - *
: : E "3 <
%"
E E -*" < 1 * < E " < E *-* 1 <
E %) <
"
*?1<-'++.,( E ** <
* / 0>> 0>%%<%
0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .:" 1 3 % " - * 1 3 % " - *
: :
E "< E )1) %" <
11 E 3" < "
E -" <
E -3" < E ) <
E *3"<
E E -*1 < -3)<
"0; ./ 0>> 0>%%<% 13"#./ 0
0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .:" 1 3 % " - * 1 3 % " - *
: :
E )" < 11 *3" E *3" <
E %"< E" -3" < "
. : "#: . ** : *"<1.
%./ 0>> 0>-*
E < 3" *3" ** E *3" <
E %" <
E" -3" < "
. : "#: . : *"<1.
./ 0 0>> 0>-*
0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .*:" 1 3 % " - * 1 3 % " - *
: : E E " < )-<
*3"
E 11<
E" -1 E < " " <
E <
E 11 < E 1*<
E % < E " <
E E "< " <
E 3"<
E )**< E )%< E 13"<
) ./ A 0>> 0>%%<% 0. ; :> *3"#./ 0 . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .-:" 1 3 % " - * 1 3 % " - *
: :
E E -1 3* < < E -- <
./ 0>> 0>0
E E " * < < E 11 = %" <
E *3"<
*0 0>> 0>0
0. ; :> . ; @0 ?1? 0 > : 0 ./ 0> 0 > . ; 0 0 . 0 0 " :
0 > /: / > .: . 0 B ; ;.0 : A C . D ;.0 :. ;. .; : = * < C . D . 0 0 ; 0>< ;.>< .":" 1 3 % " - * Girder Mountain Bike Fork Lindenberger
LOADING CONDITIONS
The assumed worst case scenario for this project is assumed to be a four foot fall. This condition assumes a total weight of 225 pounds for the rider and bike. The force of this fall is expected to go directly into the front fork itself. Landing solely on the front wheel is an undesirable loading condition. It is one that often leads to rider injury and damage to the bicycle. The most typical failure happens where neck tube meets the fork tubes. The loading condition described above would often lead to this joint failing. This failure point can be seen in Figure 4 above.
While this loading condition is undesirable it is one that can happen and as such it must be accounted for. The First step is to calculate the force going into the fork from the four foot fall.
The first step in this process involves finding velocity of the falling bodies.
= 2 ℎ
= 2 32.2 4
= 16.04 /
The Next Step is to develop an appropriate time frame for the impulse and momentum equation. To do this the potential energy for the system was calculated
= ℎ
= 225 4
= 900
This force was then plugged into the impulse and momentum equation to get an estimation of what the timeframe should be.
+ ∆ = 225 16.04 +900∆ = 0 32.2 ∆ = 0.1245
36 Girder Mountain Bike Fork Lindenberger
This timeframe was then adjusted to 0.15 seconds due to the fact that there would be some dampening in the system as well as to take into account inconsistencies that might arise from using the potential energy into the system. Plugging this new timeframe into the impulse and momentum equation the final force into the system could be found.
+ ∆ = 225 16.04 + 0.15 = 0 32.2 = 749.8
This 750 pound force was then used to find the reaction forces at the two upper pin joints. This raises some complications as the fork is a statically indeterminate system. Because of this the pin forces in the X-Axis had to be estimated. An estimate of 130 pound force for each roughly created equilibrium in the system. The Resultant forces at each point can be seen in Figure 13 below.
1100 lbf
130 lbf
130 lbf
400 lbf
750 lbf
Figure 13: Loading Conditions
Due to the fact that the resultant forces were calculated using estimations for the force in the X direction, the force in the calculations and COSMOS simulations must be adjusted. However the previous numbers do serve as a good starting point.
37 Girder Mountain Bike Fork Lindenberger
DESIGN ANALYSIS
HAND CALCULATIONS
Several parts only went through hand calculations. This was the case for the shear of the Neck Tube, the shear of the Pivot Pins, and the critical load for buckling the fork tubes. These conditions can be difficult to set up and run in COSMOS and based on the factor of safety calculated for each it was determined to be unnecessary.
Fork Tube Buckling
= 2.10 15.565 = 32.69 √1.25 + 1.125 = = 0.42 4 = 32.69 = 0.42 6061 − 6 = 10 10
6061 − 6 = 40,000
2 =
2 10 10 = = 70.25 40000 1.25 − 1.125 = = 0.0412 64 = 10 10 0.0412 = = 3456.4 32.69 With a Pcr of 3456.4 pounds, there is a 4.6 factor of safety against buckling with a 750 pound force applied to the fork tubes.
38 Girder Mountain Bike Fork Lindenberger
Double Shear
There are four pivot pins in the system and all are exposed to double shear along with the neck tube and shock pins. The following calculations focus solely on the pivot pins. It is important to note that the same steps and equations were also used to calculate the shear stress on the neck tube and shock pins.
The yield of 4130 steel is 63,100 PSI. A safety factor of two was then applied to this resulting in a yield of 31,550 PSI. From the loading conditions above, the largest force into the pins is the 1100 pound force. This information was then plugged into the shear equation to determine the smallest diameter pin required.
= 1100 31,550 =
= 0.0348 = 0.0348 = 2 4 = 0.149 The current design of the fork uses 0.3125 inch diameter pins. The shear stress of the existing pin design was then calculated to get the factor of safety.
1100 = = 7174.5 0.3125 2 4 Based on this value there is a factor of safety of 8.8.
For the neck tube and shock pins only the last equation was used. This is because both of these parts must interface with standard component. Therefore their dimensions are already known, but their factor of safety needed to be calculated. For the neck tube it was assumed that each connecting link would transfer a 260 pound force into the neck tube which results in a 520 pound force total. The resulting shear stress is 1202 PSI and gives a factor of safety of 33. The calculations on the shock pins revealed a maximum load 22,825 pounds which significantly beyond anything that the fork would actually be exposed to.
39 Girder Mountain Bike Fork Lindenberger
COSMOS SIMULATIONS
COSMOS simulations were run on parts with complicated geometry or complex loading conditions. Examples of this are the upper and lower shock mounts. Both of these parts would be difficult to perform accurate hand calculations due to the loading conditions and their shapes. Bothe of these parts returned lest than desirable safety factors. As such a detailed analysis can be found in the following section of this report.
Other parts that received COSMOS testing were the connecting links and the Upper and Lower blocks. COSMOS data for these parts can be seen in the following figures.
COSMOS testing for the connecting links was conducted under the following conditions. One end was fixed and a 260 pound force in compression was applied at the other end. Only the lower link was tested due to the fact that it is longer which increases the likelihood of buckling. A 260 pound force was used because it assumed that all of the resultant X-axis forces are only going through one point. The 1100 and 400 pound forces shown above were ignored because both ends of the connecting links are pin connections and are allowed to rotate. This eliminates bending in the link. A maximum stress of roughly 2,500 PSI is observed in the link under this condition. This results in a factor of safety of 29. Stress and displacement can be seen in Figures 14 and 15 below.
Figure 14: Lower Link Stress
40 Girder Mountain Bike Fork Lindenberger
Figure 15: Lower Link Displacement
The same 260 force was applied to the upper and lower blocks. Once again the 1100 and 400 pound forces were ignored as they would not be transferred into these parts. These forces would only cause the upper and lower links to rotate. However the forcers acting along the X-axis will go directly into the upper and lower blocks. The stress and displacement for each of these components can be seen in Figures 16 through 19 below.
Figure 16: Lower Block Stress
41 Girder Mountain Bike Fork Lindenberger
Figure 17: Lower Block Displacement
Figure 18: Upper Block Stress
42 Girder Mountain Bike Fork Lindenberger
Figure 19: Upper Block Displacement
Based on the COSMOS data for both stress and displacement, these parts are robust enough for the expected worst case scenario loading conditions. The lower block has a factor of safety of 83.The upper block has a factor of safety of 50
43 Girder Mountain Bike Fork Lindenberger
FACTORS OF SAFETY OF CONCERN
As previously mentioned the size of the shock caused some mounting issues. As such the only items that were seriously impacted were the upper and lower shock mounts. In the figures below it is clear to see that both shock mounts are close to the yield strength of the 6061-T6 that they are made of. The loading conditions for the shock mounts assumed that the entire 750 pounds force from the impact go directly into the mounts. That is to say that the shock is completely locked for whatever reason. Possible reasons for this are that the user is using too thick of shock oil, the spring is too stiff, or the shock is seized in the body.
In the case of the fork sub-assembly shown in Figure 20, a maximum strain of roughly 25,000 PSI. This provides a safety factor of just 1.6. This is much lower than that of the other components that were run through COSMOS. Displacement of the fork tubes at wheel axle is 0.4 inches. Initially this number seems high. However it is over a16 inch length and the stress in the fork tubes is roughly at 12,000 PSI so this displacement was considered to not be an issue. A secondary buckling simulation returned similar results to those shown below.
Figure 20: Fork Sub-Assembly Stress & Displacement
Based on the COSMOS testing it is clear that circular fork tubes are not the best design. This would explain why most existing girder forks use a triangular or oval layout to increase the strength in one direction. One of the early design ideas for Design 2 was to use rectangular tubing. However the only affordable supply rectangular tubing used 0.125 inch thick wall. This resulted in a much heavier design which did not meet the seven pound weight limit.
44 Girder Mountain Bike Fork Lindenberger
The upper shock mounts shown in Figure 21 and 22 were also very close to the yield of the material. Ribs were added to the bottom edge of the shock mounts. This successfully lowered the stress seen in these members but is still relatively high returning a safety factor of roughly 1.7.
Figure 21: Upper Shock Mount Stress
45 Girder Mountain Bike Fork Lindenberger
Figure 22: Upper Shock Mount Displacement
The loading conditions on these components represent the worst case scenario. It is doubtful that the shock would be completely seized so the stress going into both mounts will likely be less. In addition it is likely that the fork tubes themselves may bend under this force but they will not break. This will ensure maximum safety for the rider.
46 Girder Mountain Bike Fork Lindenberger
COMPONENT SELECTION
As the weight of the fork became the primary concern it dictated what materials should be used in the construction of the fork. As such aluminum was selected as the primary building material. However not all aluminum is the same. This is where the manufacturing process came into play. For parts that are only machined 7075-T6 aluminum was selected for its superior yield strength. For parts that are to be welded 6061-T6 was chosen for its superior weldability. In addition to production method, the availability of a specific form of the material was also a factor. For example a 1.25” O.D. aluminum tube is less expensive and easier to find in 6061-T6 than 7075-T6.
Aluminum could not be used for all components. The rotating components such as the pivot pins and shock pins will be made from 4130 cold rolled steel due to its good impact and abrasion resistance. 4130 also offers better corrosion resistance than that of 1012 and is less costly than stainless steel. 4130 will not provide the same corrosion resistance that stainless steel provides.
Bushings must be used in places where the pivot pins are in contact with rotating components. Bushings were chosen over bearings for two reasons. Bushings provide easier maintenance and cleaning and do not take up as much space as bearings. For this application SAE 863 bronze bushings were chosen. SAE 863bushings are impregnated with SAE 30 oil to lower friction. They also contain more iron for improved strength over other bronze bushings
The shock selected was a Manitou Metel R series shock and features tunable dampening, adjustable rebound, and replicable spring sets in a variety of weights. The Metel R shock also features a 3 inch stroke length. The primary reason this shock was chosen was due to its low cost and long stroke length. However this shock does create some concerns when it comes to mounting due to its 9.44 inch length.
47 Girder Mountain Bike Fork Lindenberger
BILL OF MATERIALS
The following bill of materials represents all raw materials needed to create the initial prototype for this fork. In some cases the raw material is free of charge or has been donated.
Table 3: Bill of Raw Materials Item Description Qty Unit Cost Cost 1 Shock 1 $135.00 $135.00 2 4130 Ø0.3125 x 24" Rod 1 $2.77 $2.77 3 SAE Bronze Bushings 20 $0.62 $12.40 4 5/16 Nut 10 $0.05 $0.50 5 5/16 Washer 2 $0.13 $0.26 6 4130 Ø0.75 x 12" Rod 1 $5.62 $5.62 7 Sock Head Cap Screws 2 $0.28 $0.56 8 7075-T6 12"x12"x0.375 Plate 1 $69.43 $69.43 9 6061-T6 12"x12"x0.375 Plate 1 $46.04 $46.04 10 6061-T6 12"x12"x0.1875" Plate 1 $23.71 $23.71 11 6061-T6 Ø0.75" x 12" Rod 1 $4.68 $4.68 12 6061-T6 Ø1.00" x 12" Rod 1 $8.31 $8.31 13 7075-T6 2.125"x2.5"x0.75" Block 1 $26.90 $26.90 14 6061-T6 Ø1.25"xØ1.08"x24.5" Tube 2 $20.62 $41.24 15 6061-T6 Ø1.125"xØ0.875"x12" Tube 1 $9.11 $9.11 16 6061-T6 Ø1.125"xØ1.00"x12" Tube 1 $7.91 $7.91 17 6061-T6 2.125"x2.125"x0.84" Block 1 $15.80 $15.80 18 Nylon Bar Ø0.75" x 12" 1 $4.20 $4.20
Subtotal $414.44
Shipping (5%) $24.87
Grand Total $439.31
The detailed bill of materials listing all of the detail parts required to build the fork is located in the drawings section of this report.
48 Girder Mountain Bike Fork Lindenberger
PROTOTYPE BUDGET
The comprehensive bill of materials above provides a final cost of all raw materials needed. This BOM does not include items such as surface finishes or other operations that may require an outside vendor.
The bicycle, some raw materials, and most of the hardware are already available free of charge. This represents a cost savings not shown in either budget. There is currently a $150 surplus in the budget for this project after the cost of the bicycle is removed. This $150 will allow for any unforeseen expenses such as needing more material or outside vendor costs. As such the initial budget is still fairly accurate.
Table 4: Prototype Budget Forcasted Final Component & Materials Description Supplier Budget Cost Mountain bike $200
Front Shock $150
Fork $150 Fork Tubes Tripple Tree Brake Mounts Wheel Mounts Connecting Bars
Hardware $50 Misc nuts and bolts Bearings/ Bushings
Surface Finishes $75
Misc Expenses (20%) $125
Subtotal $750
Shipping (5%) $38
Grand Total $788
49 Girder Mountain Bike Fork Lindenberger
The final cost of the fork came in at $341.18. This represents a $172 savings over the initial projected prototype cost. Some of the cost savings measures are outlined in manufacturing section of this report. However none of these costs include labor. Please see Appendix F for the running budget.
Table 5: Final Prototype Cost Total Material Cost of Prototype Description Cost Shock $135.00 Bushings $22.43 Raw Material $183.75
TOTAL: $341.18
50 Girder Mountain Bike Fork Lindenberger
SCHEDULE
The initial schedule for this project was completely over ambitious. There was not adequate time built in for redesign and optimization or even calculations and COSMOS testing.
Planned completion for this project is June 4st 2012. The schedule below shows that fabrication and assembly should be complete by May 5th. Planned field tests are to be completed between May 9th and May 19th weather permitting. Table 5 provides some key and milestone dates that need to be met along the way Please see Appendix E to see the running schedule.
Table 6: Schedule Activity Start End Concept Development 1/1/2012 2/9/2012 Proof of Design 1/6/2012 1/6/2012 Calculations and Design 1/1/2012 2/9/2012 Material Selection 1/14/2012 2/2/2012 Winter Report 3/9/2012 3/9/2012 Order materials 3/10/2012 3/29/2012 Fabrication 3/18/2012 4/28/2012 Final Assembly 4/29/2012 5/5/2012 Field Test 5/9/2012 5/19/2012 Final Report 6/4/2012 6/4/2012
51 Girder Mountain Bike Fork Lindenberger
MANUFACTURING
All manufacturing processes in the production of the prototype fork were carried out at the University of Cincinnati’s Victory Parkway machine shop. This provided a great learning experience and pointed out some flaws in the design. These flaws will be covered in the Design Modification section below.
MACHINING
Every component of the fork required some degree of machining. Some of the less complex components, such as the fork tubes, only need a few holes put in. This was accomplished by placing the tube in a vice and setting a 0, 0 location with an edge finder. The holes were then put in the correct locations using an end mill. This same process for setting 0, 0 locations was used for all parts that were machined on a mill. Figure 23 below shows an example of setting the zero location on one of the brake mounts. In this particular case this was done to properly position the mating surface on the brake mount.
Figure 23: Setting the 0, 0 for a part
Additional tools used on the mill included drills, counter bore cutters and reamers. Drills were typically used to create pilot holes. A large drill had to be used to make the holes in the upper and lower blocks for the neck tube. This was done because the machine shop did not have a 1.125” end mill. These large holes required several incremental steps in size. Slow speeds and proper cooling were also important to lower tool chatter which could cause the hole to be oversize. The counter bore cutter was used to recess the screws for the clamping features. The reamer was used on holes that required press fit bushings. A 0.0005” undersize reamer was used so that the bushings required an arbor press to put in place. It was important
52 Girder Mountain Bike Fork Lindenberger
that the hole prior to reaming be 1/32” under nominal.
Not every milling operation was completed in a conventional mill. The clamping features had to be created on a horizontal mill using a slitting saw. This process can be seen in Figure 24 below.
Figure 24: Slitting Saw on a Horizontal Mill
This provided a great learning experience. Due to the layout and age of the horizontal mills, climb milling is not recommended. However climb milling was used while cutting the original upper block. As a result the slitting saw jammed up in the part and broke into several pieces. Additionally the broken blade left took a large chunk of material out of the part. The upper block would have to be remade. This was the largest set back during the manufacturing process. Luckily no one was injured when the tool broke. The scrap upper block and broken tool can be seen in Figure 25 below.
53 Girder Mountain Bike Fork Lindenberger
Gouge in part
Broken Slitting Saw
Figure 25: Damaged Part and Broken Slitting Saw
Additional components such as the pivot pins and brake pins were manufactured on a lathe. This process was fairly straight forward. Special care had to be taken during the first few passes to check if the lathe used dimetral or radial measurement systems. The speeds and feeds were increased for the rough cut passes. Additionally a larger cut could be made during the roughing passes. This greatly reduced machine times. To get a smoother surface finish the feed rate was slowed down.
Figure 26: Turning a Brake Pin
54 Girder Mountain Bike Fork Lindenberger
External threads were created using a self feeding tail stock attachment that contained the die. This can be seen in Figure 27 below.
Tail Stock
Die
Work Piece
Figure 27: Self feeding Die Tail Stock
The tailstock was advanced onto the work piece. Once the threads of the die started cutting the tail stock automatically advanced. Once the correct length of the part was threaded the lathe was stopped. The tail stock was then pulled out of the die holder and the die could be unscrewed from the part.
WELDING
Several components of the fork required welding before they could be called complete. These components are the upper block, upper shock mounts and most importantly the fork tube sub-assembly. As previously mentioned these components were manufactured from 6061-T6 aluminum due to the fact that it is easily weldable.
The most important part of welding aluminum is the surface preparation. Any and all surface scale, oxidization, or other impurities had to be removed as it could cause cracks or voids in the welds which would lower their strength. Surface preparation was accomplished by using acetone and clean stainless steel wire brush. Acetone was used because it does not leave a film or residue on the part. Acetone also does an excellent job of dissolving dirt and oils that may have been left on parts during the manufacturing process.
After all the parts were cleaned assembly began. The first step was to press the fork bushings into the corresponding holes on the fork tubes. These parts were designed to have a press fit for proper alignment thus eliminating the need for fixtures. Next the cross links and lower shock mounts were welded in place. This was done by placing the pivot pints in the
55 Girder Mountain Bike Fork Lindenberger
fork bushings. This aligned the two sides of the fork and put the cross links in the correct locations. This can be seen in Figures 28 and 29 below.
Figure 28: Initial Weld Set-up
Figure 29: Welding Fork Sub-Assy
After the cross links and lower shock mounts were welded in place, the wheel brackets were welded on. Proper alignment of these components was accomplished by clamping the wheel to the brackets. The wheel was then centered between the two fork tubes and the brackets were tack welded in place. The wheel was then removed and final weld passes were preformed. The brake mounts were welded in place using a similar process as the wheel mounts.
56 Girder Mountain Bike Fork Lindenberger
The Upper block and upper shock mounts proved to be the most difficult components to weld. This is because the combination of these three large components quickly dissipated the heat from the welding torch. This caused low penetration between these components. The first attempt actually broke off while cleaning up the welds. Because of this a large chamfer was added to all the components to aid in welding. Low penetration discovered during the clean up stage of this second pass. A third pass was performed with more heat and additional filler as a void was also discovered.
Upper Block
Upper Shock Mount
Figure 30: Upper Block Weld Set-up
Figure 30 above shows the setup for welding the upper shock mounts to the upper block. One side of the shock mount was set on a flat surface. The upper block was then positioned and tacked in place. It was then flipped over and the other shock mount was correctly positioned using the upper shock pin. This ensured that the pin holes were properly aligned. It was then tacked in place. The shock pin was then removed and final welding was done along the outside edges.
All welding was performed by one of the machine shop’s student workers. This was done to lower cost and because the designer has little experience in welding aluminum. While the welds were not of professional quality they were deemed good enough for a prototype.
PLASMA CUTTING
The most exotic process employed for the creation of the prototype fork was CNC plasma cutting. This was chosen because it was readily available and reduced machining time. Plasma cutting was performed on a 3/8” 6061 T6 aluminum plate. Figure 31 below shows all the components that were created using the CNC plasma cutter.
57 Girder Mountain Bike Fork Lindenberger
Figure 31: CNC Plasma Cut Components
It is important to note that plasma cutting is not the best method for cutting aluminum. A very rough edge was left by the plasma cutter. This edge was also tapered going into the plate. For instance, holes on one side of the plate were much larger than the corresponding hole on the other side of the plate. Figure 32 below shows the difference between a raw part from the plasma cutter and one that had the edges cleaned up on a mill.
Plasma Cut Part Machined Part
Figure 32: Plasma Cut vs. Machined Edge
Due to the rough edge left behind by the plasma cutter, all mating surface of plasma cut
58 Girder Mountain Bike Fork Lindenberger parts had to finish machined on a mill. This includes welded surfaces and holes. Precautions were taken before any components were cut. All the holes in the plasma cut file were drawn undersize to allow for proper clean-up. This was also done on external edges where necessary.
DESIGN MODIFICATIONS
As with any prototype there are bound to be some modifications along the way. The Cad model did a fair job with eliminating interference issues. However there will always be issues to be resolved once the product makes it into the physical world. This is because of tolerance stack up, machine capabilities, or any number of other reasons.
One of the major design modifications was a change in material. Initially 7075 was going to be used on several components. However to reduce cost and the amount of scrap 6061 was used thought the fork. Additional COSMOS testing showed that this did not significantly change any stresses or displacements within these parts. Additionally all parts made from plate material were cut from a 0.375” plate of aluminum. The initial design called for some pieces to be 0.1875” aluminum. By making these few parts out of thicker material the prototype cost was reduced.
The fork sub-assembly also saw some modifications. The outer diameter of the fork bushings was increased to 0.75” to allow more material for the welding process. Additionally the cross links would no longer go through the fork tubes. These holes were eliminated to increase the strength of the fork tubes. Instead the cross links were mitered to create a strong joint. These modifications can be seen in Figure 28 in the welding section above.
The shock pins also saw some modification. The initial plans called for an external thread for a nut. This was changed to an internal thread for bolt. This was done because it was easier to cut threads for a bolt. The die that would have been used for the external threads would not have cut enough threads on the small portion of that shaft that required threads. These threads could have been cut on a lathe, but this would have required a time consuming set up that might have resulted in the same problem as the die.
To ensure that the fork is rigidly mounted to the bike a clamping feature was added to the upper block. This was done to keep the upper block from rotating on the neck tube. Initially this joint was designed to be a press fit joint. However due to the tooling that was available at the shop it was impossible to achieve press fit dimensions. Additionally a star nut was also added to the bottom of the neck tube. The star nut is pressed into the next tube. A washer with a screw in it then pulls the neck tube through the frame and tight against the lower block. Star nuts are common equipment on most bicycles. It ensures that the fork bearings are fully seated against their races eliminating any steering slop.
59 Girder Mountain Bike Fork Lindenberger
HIGH VOLUME PRODUCTION
Prototypes rarely share the same manufacturing as their mass produced counterparts. That is because there is a large cost and time frame associated with developing production tooling. The prototype developed for this project was no different. All the components were manufactured by machining. Machining is typically a costly and time consuming manufacturing process. For high production values the time spent on machining operations should be limited.
For this particular product, most of the components could be quickly and easily manufactured using castings and forgings. Water jet cutting would also be used over plasma cutting. Many of the complex parts such as the upper block could be quickly and easily manufactured as one part with casting. For the prototype the block and shock mounts were separate components that had to be welded together. Casting would eliminate a welding operation as well as increase joint strength. Some secondary machining operations would be necessary to clean up the bearing surfaces, hole for the neck tube, and to add the clamp feature. However this machining time would be drastically less than if the part was machined from one solid block. Components such as the connecting links perfect for forging operations. This would greatly increase their strength. Water jet cutting would be used because it would drastically lower the amount of secondary machine required. It might even be possible to completely eliminate secondary machining on these components. This is because water jet cutting leaves a much smoother and straighter edge than a plasma cutter.
The other major change from prototype to mass production manufacturing would be the introduction of fixtures and jigs for welding and machining. Jig would be required for secondary machining operations on cast and forged parts. Welding fixture would greatly increase productivity as well. Most of the time spent welding the prototype was spent making sure that the components were properly aligned.
The last major advantage of mass production is lower material cost. This is because material cost drops when ordering in bulk standard sizes. For the prototype material had to be ordered as special lengths. This required the supplier to cut it to the proper length. This added a cut cost to the material cost. Switching to metric hardware would also make mass production easier. Only one set of tools would be needed for assembly. The prototype has a mixture of standard and metric hardware. Components that were from the stock bike are metric where as designed components used standard hardware. This was done mainly because the machine shop had a larger selection of standard taps and dies which made manufacturing easier.
60 Girder Mountain Bike Fork Lindenberger
TESTING
Testing was performed on two fronts. First was to verify that all of the product objectives were met. Next was the riding test which revealed how the fork performed.
The adjustability of the fork is solely dependent on the shock that was selected. The Manitou Metel R shock has a wide variety of springs with different rates to choose from. These springs range from 250 pounds per inch all the way up to 700 pounds per inch. Additionally the spring preload is also completely adjustable. To tune the chock even further different weight oils can be used within the shock. The shock body also features a valve to fine tune the shock rebound rate.
The fork no longer features completely interchangeable fork tubes. However in a production environment the different components would be made available individually.
The actual cost of the prototype was $341.18. This is less than half of the initial estimate. This price would drastically fall in a mass production environment. This in primarily due to the cost savings associated with buying material in bulk. A consumer price tag below $300 could be easily reached.
As far as durability goes the fork survived all the testing it was put through. It did however develop some lateral wobble. This is most likely due to the way that the links are connected to the fork. At the frame the connecting links are tightened against the upper and lower blocks. However, on the fork sub-assembly the connecting links are not tightened against any surfaces. Nylon bushings hold the links in place. See Figure 33 below for lateral wobble.
61 Girder Mountain Bike Fork Lindenberger
Figure 33: Fork Wobble Direction
Easy Maintenance was another key feature for this prototype. The entire fork can be disassembled with a few hex keys, a pair of pliers, and an adjustable wrench. Six bolts are removed and their respective pins can be removed. This will leave only the neck tube with the upper and lower blocks on the frame. Time required for complete assembly was 45 minutes without the aid of another person. Maintenance should be limited to removing the dirt around pivoting joints and applying a light coat of oil.
The fork was tested in wet and muddy environments. These conditions did not cause any binding or other negative effects.
Weight was a major factor for the fork. The maximum weight allowable was seven pounds. This was value was chosen because no mountain bike forks could be found above this weight. Even with the thicker material used on several components the final weight was 6.866 pounds. Figure 34 below shows the fork with all standard components being weighed.
62 Girder Mountain Bikee Fork LindenbergerLind
Figure 34: Weighing the Fork
The prototype was paintedainted black to match the bike it was mounted. All edgesed were also ground smooth. All weld joints were also smoothed out. All of this preparationaration gave the fork a very professional appearancearance. This can be seen in Figure 35 below.
Figure 35: Fork Installed on Bike
The fork was designeded to fit all bikes that use a 1.125” steerer tube. AdditionallyAddit a bushing was made to accommoommodate bike using tapered steerer tubes. Theseese taperedtap tubes are 1.25” at the bottom and 1.125” at the top. By designing the fork around these commonc sizes, it ensures that it will fit the larglarge majority of mountain bikes on the market.
Testing proved that the forfork is compact enough to not cause binding issuesissue on any cables. Steering was also not ddisrupted through the normal range. At a certaertainin point the fork tubes will come in contactct with the frame of the bike. The fork does providevide a steering range
63 Girder Mountain Bike Fork Lindenberger
greater than 180 degrees. This was deemed acceptable as most people do not have a need to turn the wheel further than that.
The second half of the testing phase involved performing a riding test. This would provide results on how the fork handled. This includes how the steering feels and how well the suspension works. To get accurate data several people were asked to ride a bike with the fork mounted to it. These people had a wide range of experience with bicycles. Some were recreational sport riders, others had not ridden a bicycle since childhood, and some were ex- BMX racers. The general consensus was that no discernible difference could be noticed between the girder for and the standard fork on flat pavement. This makes since as the girder fork places the front axle in the exact location that the stock fork would have. Only the more experienced riders pick up on the wobble in the fork.
The suspension test on the other hand provided some unexpected results. Even with the stiff 250 pound per inch spring installed bumps and impacts felt soft and subdued. This is most likely because to the girder suspension system. In a normal telescopic fork all of the impact force is directed linearly into the rider. With the girder system the fork tubes are not directly connected to the handle bars. The forces are rotationally directed into the shock and handle bars through the connecting links. It is unclear if this is a good or bad feature based on the limited test sample. It is most likely a feature that riders will love or hate depending on their riding style. The consensus of the test group was that this was a good feature for riding on pavement and the light off road use that the prototype saw.
Heavier testing was not performed due to a general lack of confidence in the welded joints between the upper block and upper shock mounts. The reason for this is outlined in the welding section of this report. It was also deemed too dangerous for a human rider to test the fork to its limits.
64 Girder Mountain Bike Fork Lindenberger
CONCLUSION
The project has mostly been a success. One of the major concerns is still the shock mounting brackets. These are the weakest members in the system. Knowing this, it might have been a better idea to purchase a smaller shock and work out some sort of progressive shock system. That is to say that the shock would not be fixed to a stationary point at one end. This would involve connecting the shock to the upper and lower links in a way that would allow for longer suspension travel with a shorter shock stroke length. The other option would be to adapt the design for a road bike. Less suspension travel is required on a road bike. The stress going into the system would have been much lower as well.
The fork tubes themselves pose somewhat of a problem. In a motorcycle application rounds tubes would most likely not be used. Most use a triangular shape that reduces the problems caused by using separate wheel brackets. A triangular design would also lower the displacement due to bending that was seen in the COSMOS simulations of the fork sub- assembly. A Rectangular tube design would drastically reduce the possibility of bending the fork.
The biggest problem that came about during testing was the lateral wobble. This would defiantly cause problems at high speeds. A second prototype you need to be developed to eliminate this issue. It is believed that by revising the way the connecting links attach to the fork sub-assembly this can be accomplished. These links need to be directly bolted to a surface rather than relying on spacers as is the current method.
Overall this project has been a great learning experience on several fronts. Proper research is important to make sure that the new design does not repeat problems that may be associated with existing problems. Computer designs can only go so far. A product may work perfectly on a computer screen but problems will present themselves once the prototype is built. The actual manufacturing process will also quickly point out where the design needs to be modified to facilitate the manufacturing process. A good knowledge of each of these twill lead to a successful design.
65 Girder Mountain Bike Fork Lindenberger
WORKS CITED 1. Surly 1 X 1 Rigid Mountain Bike Fork. CambriaBike.com. [Online] 2011. [Cited: September 26, 2011.] http://www.cambriabike.com/shopexd.asp?id=14662&page=Surly+1+X+1+Rigid+Mountain +Bike+Fork. 2. Wardenaar, Nic. Breathing life into those old Girvin forks. Lets Ride. [Online] April 13, 2009. [Cited: September 26, 2011.] http://aridesomewhere.blogspot.com/2009/04/breathing- life-into-those-old-girvin.html. 3. Manitou Minute Expert Suspension Fork. CambriaBike.com. [Online] 2011. [Cited: September 26, 2011.] http://www.cambriabike.com/shopexd.asp?id=128656&page=Manitou+Minute+Expert+Sus pension+Fork. 4. Motorcycle Front Ends. A View on Custom Motorcycle Design and Building. [Online] WorldPress. [Cited: November 14, 2011.] http://designandbuildingcustommoto.wordpress.com/2011/03/26/motorcycle-front-ends/. 5. Crowe, Paul. Yamaha R1 Aluminum Girder Front Suspension from SuspensionSmith of Australia. The Kneeslider. [Online] October 10, 2011. [Cited: November 14, 2011.] http://thekneeslider.com/archives/2011/10/17/yamaha-r1-aluminum-girder-front-suspension- from-suspensionsmith-of-australia/. 6. Bliemeister, Matt. Loveland.
66
APPENDIX A - RESEARCH
Interview with customer, Sept. 26, 2011
Matt Bliemeister, BMX Team Manager/Repair, Former Engineer
5632 Miss Royal Pass Dr. Loveland OH, 45140
Light weight and quality are biggest factors
Price comes after performance and quality
Modular design is important if parts are complex
Standard parts are critical
Adjustability/adaptability is paramount.
Quick change components if at all possible.
There is a point where weight becomes a major cost driver.
To shave one pound it might cost $800.
Robust http://www.cambriabike.com/shopexd.asp?id=14 Widely Available 662&page=Surly+1+X+1+Rigid+Mountain+Bik Simple Design e+Fork 9/26/11. Surley 1 X 1 Rigid Mountain Bike Fork. CambriaBike.com Strong Materials Light Weight Inexpensive No Suspension Not Modular
The Surly 1x1 Mountain fork features CroMoly tubing, butted blades and fits wide 2.7" tires with clearance.
CroMoly tubing, butted blades Suspension-corrected, fits wide 2.7" tires with clearance Has ISO disc tabs and removable canti pivots Steerer Tube: 1-1/8" Threadless Steerer Tube Length: 260.0 mm Fork Rake: 45 mm Axle to Crown Length: 413 mm Crown Race: 30.0 Front Axle Type: 9x1 Wheel Size: 26" Brake Type: Linear Pull - Canti/Disc Front Hub Spacing: 100 mm Brake Usage F/R: Front Disc Mount Type: 51mm I.S. Front Material: CrMo
Appendix A1
Simple Design Widely Available http://www.cambriabike.com/shopexd.asp?id=12 Easy to manufacture 8656&page=Manitou+Minute+Expert+Suspensi Adjustable on+Fork 9/26/11. Manitou Minute Expert Suspension Fork. CambriaBike.com Expensive Easily damaged Not modular Air Shock
A great fork communicates everything that's happening between your tire and the trail, without jarring lose any expensive dental work. In the past, though, you had to accept a weight penalty in order to gain rock-solid steering. The Minute is here to change all that with its ultra-stiff 32mm stanchions and MARS Air spring. Forget about noodly XC forks and heavy trail forks. It's time for a Minute.
Specifications: Travel: 130mm Spring: ACT Air Spring Rate: Medium Bottom Out: Rubber Bumper Steerer: 1 1/8" Steel Crown: Forged I-Beam Crown Crown Finish: Black Ano Offset: 41.27 Compression Damping: TPC Technology, Absolute+, Trail Tuned Rebound Damping: Adjustable TPC Adjustments: Air, Compression to Lockout, Rebound Leg Diameter: 32mm Leg Material: Straight Wall AL Wheel Size: 26 Brake: Post Mount Axle: 9mm Crown to Axle: 458 / 478 / 508 Colors: Black
Appendix A2
Solid Fork Tubes http://aridesomewhere.blogspot.com/2009/0 Adjustable Suspension 4/breathing-life-into-those-old-girvin.html 9/26/11. Breathing life into those old Not Modular Girvin forks. Lets Ride! Complex/Poor Design Poor OEM Shock Company went out of business Maintenance Difficult
Girvin / Proflex / Noleen Girder Fork
Little Tech Specs are known for these forks as all companies are out of business. Knowledge of these forks comes from reviews and blog posts.
Custom Design http://thekneeslider.com/archives/2011/10/1 Requires Frame Modification 7/yamaha-r1-aluminum-girder-front- suspension-from-suspensionsmith-of- Rear mounted connecting links australia/ 11/14/11. Yamaha R1 Aluminum Self-centering design Girder Front Suspension from Might limit turning angle SuspensionSmith of Australia. The Kneeslider.
Custom designed Girder Motorcycle fork. This is a one off fork and required some modification to the motorcycle frame. One unique feature of this fork is that the connecting links are connected to the handle bars behind the steering axis. This provides more suspension travel and a compact design. It also helps the fork self-center.
Appendix A3
Geometry of Bike Handling. Calfee Design. [Online] [Cited: November 14, 2011.] http://www.calfeedesign.com/tech- papers/geometry-of-bike-handling/
This website provides good insight into standard values for rake, trail and other geometric features of a bicycle.
Motorcycle Front Ends. A View on Custom Motorcycle Design and Building. [Online] WorldPress. [Cited: November 14, 2011.] http://designandbuildingcustommoto.wordp ress.com/2011/03/26/motorcycle-front- ends/.
This website provides a wealth of information regarding different motorcycle forks. Some pros and cons are listed for each type of fork design. In addition to that some of the following pages go into fork geometry. It covers how to measure and change each feature as well as some common issues that arise with these modifications.
Appendix A4
APPENDIX B – CUSTOMER SURVEY AND RESULTS
MODULAR GIRDER MOUNTAIN BIKE FORK CUSTOMER SURVEY
The purpose of this survey is to discover if there is any interest in a modular girder suspension mountain bike fork. The primary objective is to have a suspension fork tubes can easily be changed depending on the environment or if damaged rather than buying a new for assembly. This fork design would also allow the user to quickly and easily go from a 26” bike to a 29” or any other size for that matter.
How important is each feature to you in the design of a Girder Mountain Bike fork? 1 = low importance 5 = high importance Average Affordable 1 2 3 4 5 N/A 3.8 Modular 1 2 3 4 5 N/A 3.2 Light Weight 1 2 3 4 5 N/A 4.2 Durable 1 2 3 4 5 N/A 4.8 Adjustable 1 2 3 4 5 N/A 3.8 Compatible 1 2 3 4 5 N/A 3.5 Compact 1 2 3 4 5 N/A 3.5 Easy Maintenance 1 2 3 4 5 N/A 4.3 Appearance 1 2 3 4 5 N/A 3.7 Work in several environments 1 2 3 4 5 N/A 4.3 How satisfied are you with your current Mountain Bike fork? 1 = very UNsatisfied 5 = very satisfied Average Affordable 1 2 3 4 5 N/A 3.5 Modular 1 2 3 4 5 N/A 3.3 Light Weight 1 2 3 4 5 N/A 2.7 Durable 1 2 3 4 5 N/A 5.0 Adjustable 1 2 3 4 5 N/A 3.5 Compatible 1 2 3 4 5 N/A 3.0 Compact 1 2 3 4 5 N/A 3.0 Easy Maintenance 1 2 3 4 5 N/A 3.5 Appearance 1 2 3 4 5 N/A 4.5 Work in several environments 1 2 3 4 5 N/A 3.7 How much would you be willing to pay for this product?
$100 - $200 $201 - $300 $301 - $400 $401 - $500 $501 - $600
Average expected price: $316
Thank you for your time.
Appendix B1
APPENDIX C – QUALITY FUNCTION DEPLOYMENT
Ryan Lindenberger GirderMountainbike Fork 9 = Strong 3 = Moderate 1 = Weak ost ($) C (Yes/No) Hardware Standardized Less than (Yes/No) 7 pounds Function (Yes/No) after Crash Frontal Material Strength (PSI) Size (Inches) Tools Common Used (Yes/No) Person One Assembly/Disassembly (Yes/No) Edges Sharp (Yes/No) No Rust Resistance Property/Surface (Material Coating) Bearings (Yes/No) Sealed importance Customer Designer's Multiplier SatisfactionCurrent SatisfactionPlanned Improvement ratio Modified Importance Relative weight Relative % weight Adjustable Size (Yes/No) Affordable 9 3 3 1 3 3 3.8 1.1 3.5 4 1.1 4.8 0.11 11% Modular 9 3 1 3.2 1.2 3.3 4.5 1.4 5.1 0.12 12% Light Weight 9 9 3 3 4.2 0.9 2.7 3 1.1 4.2 0.10 10% Durable 1 1 9 9 3 3 3 4.8 1.0 5.0 5 1.0 4.8 0.11 11% Adjustable 9 9 3 1 3 1 3.8 1.2 3.5 4 1.1 5.3 0.12 12% Compatible 3 9 9 3.5 1.0 3.0 3 1.0 3.5 0.08 8% Compact 9 3.5 0.8 3.0 3 1.0 2.8 0.06 6% Easy Maintenance 3 1 1 3 9 9 1 1 4.3 1.0 3.5 3.8 1.1 4.6 0.11 11% Appearance 3 1 9 9 1 3.7 1.0 4.5 4 0.9 3.3 0.08 8% Work in Several Environments 3 1 3 9 9 4.3 1.0 3.7 4 1.1 4.7 0.11 11% Abs. importance 2.44 3.25 0.99 1.11 2.40 2.33 2.62 1.33 1.09 0.68 2.44 1.84 22.5 43.2 1.0 Rel. importance 0.11 0.14 0.04 0.05 0.11 0.10 0.12 0.06 0.05 0.03 0.11 0.08 1.00
C1
APPENDIX D – PRODUCT OBJECTIVES Product Objectives Modular Girder Mountain Bike Fork The following is a list of proof of design agreements and how they will be obtained or measured to ensure that the goal of the project was met. The Product Objectives will focus on a modular girder suspension style mountain bike fork. It will be noted that the purchased shock is not being tested, but only fabricated items of the fork itself. Adjustable: Relative Weight 12% 3. The fork tubes are to be replaceable with a stronger material of a specific standard size. 4. An adjustable shock will be used for suspension. Modular: Relative Weight 12% 3. The fork will offer the ability to change the fork tubes to different materials and lengths as needed by consumers 4. Standardized hardware will be used where applicable. Affordable: Relative Weight 11% 2. The fork in standard equipment will cost consumers no more than $300. Durable: Relative Weight 11% 2. The fork will be designed with an appropriate safety factor so that suspension and steering functions are not damaged after a frontal crash. Easy Maintenance: Relative Weight 11% 4. The fork will be able to be disassembled and reassembled by one person with average mechanical ability. 5. Only common tools are to be used. 6. Worn or damaged hardware will be easily available through hardware stores such as McMaster-Carr. Work in several environments: Relative Weight 11% 2. The fork shall work in normal, wet, muddy, and dusty/sandy environments a. Sealed bearings shall be used where applicable to keep debris out of moving joints b. Materials selected will not corrode or rust in these environments i. If materials may corrode, a surface finish to aid in the prevention of corrosion will be employed. Light Weight: Relative Weight 10% 2. The fork in standard equipment will weigh less than 7 pounds. Appearance: Relative Weight 8% 3. The fork is to have no sharp edges which could easily injure the rider. 4. Surface finishes used will prevent corrosion and not come off easily in day to day use. Compatible: Relative Weight 8% 2. The fork will use standard neck bearings and will work on several different bikes. a. The fork will be able to be used on bikes ranging from 20” to 29”wheel size while only replacing the fork tubes. Compact: Relative Weight 6% 3. The fork will not be bulky to the point of inhibiting the steering of the bike. 4. The fork will be designed to minimize the possibility of brush getting caught in the linkages.
Appendix D1
APPENDIX E – SCHEDULE
Ryan Lindenberger Girder Mountain Bike Fork
TASKS Nov20-26 3 Nov27- Dec -410 Dec 1117 - Dec 1824 - Dec 2531 - Dec 17 - Jan 814- Jan 15 Jan -21 22 Jan -28 4 29 Jan -Feb -511 Feb 1218 -Feb 1925 -Feb 3 26 Mar -Feb -410 Mar 1117 -Mar 1824 -Mar 2531 -Mar -17 Apr -814Apr 15Apr21 - 22Apr28 - 29Apr5 May - -612May 13May19 - 20May26 - 27MayJun -2 -39 Jun Proof of Design to advisor 6 11 Concept sketches to advisor 6 11 Shock Selection 13 11 3D Modeling 13 23 COSMOS Testing 13 9 Engineering Calculations 13 9 Material Selection 13 2 Design Modification 20
Oral 1 1 Report 8 8 Order Material 27 29 Fabricate Components 28 5 Surface Finishes 5 5 Assembly 5 5 Test Telescopic Fork 19 13 Field Test Girder Fork 19 3 Demo to Adviser 7 17 Demo to Faculty 14
Oral Final Presentation 28 23 Final Report 4 4
Appendix E1
APPENDIX F – PROTOTYPE BUDGET
Planned Prototype Budget
Forcasted Final Component & Materials Description Supplier Budget Cost Mountain bike $200
Front Shock $150
Fork $150 Fork Tubes Tripple Tree Brake Mounts Wheel Mounts Connecting Bars
Hardware $50 Misc nuts and bolts Bearings/ Bushings
Surface Finishes $75
Misc Expenses (20%) $125
Subtotal $750
Shipping (5%) $38
Grand Total $788
Appendix F1
Actual Prototype Budget
Item Description Qty Unit Cost Cost 1 Shock 1 $135.00 $135.00 2 4130 Ø0.3125 x 24" Rod 1 $2.77 $2.77 3 SAE Bronze Bushings 20 $0.62 $12.40 4 5/16 Nut 10 $0.05 $0.50 5 5/16 Washer 2 $0.13 $0.26 6 4130 Ø0.75 x 12" Rod 1 $5.62 $5.62 7 Sock Head Cap Screws 2 $0.28 $0.56 8 7075-T6 12"x12"x0.375 Plate 1 $69.43 $69.43 9 6061-T6 12"x12"x0.375 Plate 1 $46.04 $46.04 10 6061-T6 12"x12"x0.1875" Plate 1 $23.71 $23.71 11 6061-T6 Ø0.75" x 12" Rod 1 $4.68 $4.68 12 6061-T6 Ø1.00" x 12" Rod 1 $8.31 $8.31 13 7075-T6 2.125"x2.5"x0.75" Block 1 $26.90 $26.90 14 6061-T6 Ø1.25"xØ1.08"x24.5" Tube 2 $20.62 $41.24 15 6061-T6 Ø1.125"xØ0.875"x12" Tube 1 $9.11 $9.11 16 6061-T6 Ø1.125"xØ1.00"x12" Tube 1 $7.91 $7.91 17 6061-T6 2.125"x2.125"x0.84" Block 1 $15.80 $15.80 18 Nylon Bar Ø0.75" x 12" 1 $4.20 $4.20
Subtotal $414.44
Shipping (5%) $24.87
Grand Total $439.31
Appendix F2 Girder Mountain Bike Fork
Ryan Lindenberger 2012 Spring Presentation Advisor: Amir Salehpour The Problem
• Existing Suspension forks only use the Telescopic design – Parts potentially easily damaged • Parts require tight tolerances – Many use air dampening • Not a modular product – If one component is damage the entire fork must be replaced Existing Products Telescopic
• Pros Typical failure – Compact point – Easy to Assemble Upper tubes rides inside • Cons lower – Requires Tight assembly. Tolerances and high surface finishes Internal Spring – Easily Damaged Air Dampening – Not Easily serviceable Existing Products – Girvin/Proflex • Pros Connecting – Compact Links – Easily Serviced – Shock Protected • Cons – No longer Produced Solid down tubes – Low suspension travel (50mm) – “J” Shaped suspension path Customer Needs
• A Well performing mountain bike fork • A Safe fork • A light Weight Fork • A durable and rugged fork • An easily serviceable fork Product Objectives
• The Primary objective is to develop a working prototype for a performance oriented Girder Fork. • Adjustable: Relative Weight 12% • Modular: Relative Weight 12% • Affordable: Relative Weight 11% • Durable: Relative Weight 11% • Easy Maintenance: Relative Weight 11% Product Objectives
• Work in several environments: Relative Weight 11% • Light Weight: Relative Weight 10% • Appearance: Relative Weight 8% • Compatible: Relative Weight 8% • Compact: Relative Weight 6% Design Iterations – Version 2
• Welded Forks • Lower Link Behind Steering Axis • Minimizes Change in Trail • Closely Mimics Geometry of OEM Fork • Light Weight Design Iterations – Version 2 Design Iterations – Version 2 Design Iterations – Version 2 Loading Conditions
V = 2gh V = (2 32 2. )( )4 V =16.09 ft / sec
− mV1 + F t = mV2 225 − (16.09) + F .0( 15) = 0 32 2. .0 15F =112.47 F = 749 8. lbf 750 lbs Loading Conditions
• Fork Tube Buckling – Pcr = 3456.4 lbs • 4.6 Safety Factor • Pivot Pins Double Shear – Shear Stress = 7174.5 PSI • 8.8 Safety Factor • Neck Tube Double Shear – Shear Stress =5084.45 PSI • 7.5 Safety Factor • Active Links – σ = 1300 PSI • 56 Safety Factor 750 lbs Factors Of Safety
• Parts built from standard raw material sizes where applicable • Leads to high Safety Factors – Allows parts to survive a large array of unforeseen loading conditions Factors of Safety
750 lbf into system: Safety Factor of 1.65: 0.4” Displacement Component/Material Selection
• Weight is a Primary Concern – 6061 T6 For all Aluminum components to lower cost (Additional COSMOS testing was performed and parts altered as needed) – 4130 For Pivot Pins – SAE 863 Bronze Bushings For Rotating Components Design Modification
• All plate aluminum pieces were made from 0.375” – Reduced cost associated with purchasing a 0.1875” plate and increased factor of safety • A clamp was added to the upper block to increase rigidity • A star nut was added to tighten the fork against the bearings in the neck – Difficult to get the fork to fully seat against the bearings by hand • The shock pins were made using internal threads rather than external – Easier to manufacture Prototype Fabrication and Assembly
• Plasma Cutting was fast and inexpensive but required time consuming clean up of edges Prototype Fabrication and Assembly
• Weld prep was done using Acetone and a Stainless Steel wire brush. This was to remove any surface impurities Prototype Fabrication and Assembly
• The importance of cutting directions Testing
• Adjustable: Shock is completely Adjustable • Modular: Separate components where applicable • Affordable: Prototype cost $342. Production fork would be well below this. • Durable: Survived small jumps (not confident in welds) • Easy Maintenance: Remove 6 bolts pins for general maintenance Testing
• Work in several environments: Tested in muddy and wet environments • Light Weight: 6.8 pounds (under 7 lb max) • Appearance: Painted to Match bike, Smooth edges and rounded corners • Compatible: Replaced standard bike fork. Will work on all bikes with 1.125” steerer tube • Compact: Does not bind or impede steering through normal range. (Grater than 180° of movement) Testing
• 10 people used the Girder fork. No noticeable difference in steering was detected • The Girder design feels softer when going over bumps even with a 250lb spring. – The force going into the rider is offset by the links rather than going directly into the rider • A small wobble developed during testing. This is a result of how the links are attached. Testing Recommendations
• Redesign to use a smaller shock. – Reduce the number of welded components and increase strength. • Develop welding fixtures to aid in assembling the fork. • Redesign they way the links are held on. – Eliminate the wobble that developed • Switch to metric to lower the number of tools required. Schedule Ryan Lindenberger Girder Mountain Bike Fork
TASKS Nov20-26 3 Nov27- Dec 4-10 Dec 11 -17 Dec 18 -24 Dec 25 -31 Dec -7 1Jan -14 8Jan 15Jan-21 22Jan-28 4 29 Jan-Feb 5-11 Feb 12 -18 Feb 19 -25 Feb 3 26 -Mar Feb 4-10 Mar 11 -17 Mar 18 -24 Mar 25 -31 Mar 1-7 Apr 8-14 Apr 15Apr -21 22Apr -28 295 Apr -May 6-12 May 13May-19 20May-26 27May-Jun2 Jun3-9 Order Material 27 29 Fabricate Components 28 5 Surface Finishes 5 5 Assembly 5 5 Test Telescopic Fork 19 13 Field Test Girder Fork 19 3 Demo to Adviser 7 17 Demo to Faculty 14
Oral Final Presentation 28 23 Final Report 4 4 Budget
Total Material Cost of Prototype Description Cost Shock $135.00 Bushings $22.43 Raw Material $183.75 TOTAL: $341.18
$172.00 below Estimated Prototype Cost Questions?